Effects of prazosin, KMD-3213, and BMY7378 on NAd-induced contraction in thoracic aortas from α1B-KO mice. Ordinate: contraction, expressed as percentages of the maximum response. Abscissa: negative log concentration (M) of NAd. Each value represents the mean±s.e. of 7–10 experiments. Aortic segments were exposed to vehicle (control) or different concentrations of (a) prazosin, (b) KMD-3213, or (c) BMY7378 before the addition of cumulative concentrations of NAd.